Pressure Drawdown Mechanism and Design Principle of Jet Pump Bit

Reducing the bottom hole differential pressure (BHDP) and so as to reduce the cuttings hold-down effect can significantly improve the rate of penetration (ROP). This paper analyzes the pressure drawdown mechanism of the jet pump bit, and then designs a novel annular jet pump bit. Using hybrid grid method, the key factors which affect the pressure drawdown capacity of the bit are discussed. The backflow below the reverse nozzle outlet is the main reason that reduces the pressure drawdown capacity of the jet pump bit. The design principle of the jet pump bit is given: the axial and radial angles are 150°-180° and 60°-75° respectively, the bit clearance should be kept below 3 mm, preferably using the vortex-jet flow combination pressure drawdown theory to reduce the bottom hole pressure, and the bit rotation speed should be as large as possible, which provide the theoretical guide for its development.